Shape memory alloys characterisation by different methods

摘要

Shape Memory Alloys (SMA) are metal materials that show the property to return to a previously defined shape or dimension when they are subjected to a variation of temperature. These alloys can be largely deformed at some relatively low temperatures and when they are brought to some higher temperatures return to their original shape. Materials that show shape memory only by means of heating are called "one-way shape memory alloys"; materials that also show the phenomenon during the cooling, are called "two-way shape memory alloys". Changing in shape or dimension is generally associated to a generated load, so that the pieces could be employed as actuators. Today Copper based alloys and Nickel-Titanium alloys are employed by exploiting this property. The property of these materials is referred to a temperature called "transition temperature". The knowledge of this temperature is very important in order to an appropriate use of the material. In this research, microstructure of a Cu-Al-Ni SMA has been studied to detect martensitic and austenitic phases, while simple tooling for experiments have been set up in order to apply the main methods to find out the transition temperatures of different Ni-Ti alloys: the results, discussed and compared, shown a very good overlapping even employed several simplifications of the tooling that make very easy the experimental procedures.